The invention relates to novel uses of D-xylose, esters thereof and oligosaccharides containing xylose for improving the functionality of epidermal cells.
It relates more precisely to novel uses of these products in the field of cosmetics and pharmacy, especially dermatology, for improving this functionality by stimulating the synthesis of proteoglycans and/or glycosaminoglycans.
Throughout the present statement, proteoglycans will be denoted by the abbreviation PG and glycosaminoglycan is by the abbreviation GAG.
If it is desired to improve skin hydration, it is possible to employs products whose action is associated with:
either an occlusive effect: this property makes it possible to regulate the water loss b) creating a barrier which opposes the passage of water molecules;
or a humectant effect: these products act bad hygroscopic;
or a keratiniocyte differentiation effect leading to skin hydration: this action culminates in the formation of corneocytes, particularly the corneocyte envelope, and to the formation of substances synthesized by keratinocytes during their differentiation;
or an effect which increases the water retention capacity of intercellular spaces: this effect can be obtained by promoting the synthesis of PG and/or GAG by skin cells, especially, keratinocytes and/or fibroblasts.
PG, formerly called mucopolysaccharides, are complex macromolecules consisting of a central protein, or xe2x80x9ccarrier proteinxe2x80x9d, substituted on its serine residues by osidic chains called GAG. These chains consist of a series of hexosamines (glucosamine or galactosarnine) alternating with another sugar (glucuronic or iduronic). In skin they are sulfated in the 2-, 4-, 6-position or on the amine group. (Structure and metabolism of proteoglycans and glycosaminoglycans, J. E. Silbert, J. Invest. Dermatol. (1982), 79, 31-37).
Like GAG, PG are secreted in the skin by keratinocytes and fibroblasts and are partly responsible for its hydration.
The organism is permanently subjected to many types of aggression from the external environment.
The skin serves to protect the organism against the external environment. The epidermis is the external barrier of the skin. It consists especially of keratinocytes, which differentiate in the course of their migration from the basal layer of the epidermis to the corneal layer of the epidermis.
One of the most important functions of this barrier, or epidermis, is to prevent water loss from the organism. Another function is to combat the various forms of physical, chemical and microbial aggression from the surrounding medium.
Water loss is largely combated by PG and GAG, which are present in large amounts in the extracellular medium. These molecules participate substantially in the hydration and mineralization (fixation of counterions) of the extracellular matrices, particularly by virtue of their capacity to fix water. They also participate actively in the correct functioning of the epidermal cells.
In particular, these PG and GAG are synthesized by keratinocytes in the epidermis.
Once synthesized by a cell, these PG and GAG remain in the extracellular matrix surrounding this cell and undergo little or no migration.
PG represent about 0.2% of the dry weight of the skin, which is low in comparison e.g. with the amount of collagen, which represents more than 75% of said dry weight (The collagens: biochemistry and physiopathology, E. J. Kucharz, published by Springer-Verlag, 1992). This is in no way a reflection of the physiological importance of PG and GAG.
In fact, by dint of their polyanionic osidic structures, these molecules have the characteristic of associating very strongly with counterions (sodium and potassium) and water molecules. They have the capacity to fix water up to 1000 times their volume, thereby forming gels. They therefore behave like natural mineralizing hydrating agents for the epidermis, particularly the epidermal cells and especially the germinal cells, the cellular basal membranes, the skin appendages, particularly the hair follicles, and also the extracellular matrices such as that of the dermo-epidermal junction (DEJ). PG and GAG therefore play a decisive part in the functionality of these cells and of the matrix to which these cells adhere.
The most abundant GAG in the skin are hyaluronic acid (50% of the hyaluronic acid in the organism is in the skin) and dermatan sulfate, while others, like chondroitin 4- and 6-sulfate, heparan sulfate and keratan sulfate, are found in smaller amounts. Hyaluronic acid is without doubt the most widely known skin hydrating agent. It is pointed out that, as distinct from the other GAG, this molecule is neither sulfated nor fixed to a carrier protein.
The epidermis contains chondroitin 4-sulfate and keratan sulfate. The dermo-epidermal junction contains chondroitin 6-sulfate and heparan sulfate, which are very important in the cohesion between dermis and epidermis. Hyaluronic acid is located principally in the basal layer and to a lesser extent in the spinous layer (Age-dependent changes of hyaluronan in human skin, L. J. M. Meyer and R. Stern, J. Invest. Dermatol. (1994), 102, 385-389).
It is also known that ageing has important repercussions on the content and distribution of PG and GAG in the skin. The epidermal distribution of hyaluronic acid is seen to fall drastically to the point where it is no longer detected in the senescent epidermis (Age-dependent changes of hyaluronan in human skin, L. J. M. Meyer and R. Stern, J. Invest. Dermatol. (1994), 102, 385-389). Likewise, a decrease is noted in the chondroitin 6-sulfate located principally in the dermo-epidermal junction (DEJ) (Patterns of glycosaminoglycan/proteoglycan immuno-staining in human skin during ageing. M. D. Willen, J. Invest. Dermatol. (1996), 968-974).
D-xylose is a well-known sugar of the 5-carbon aldose family. For its description, its sources and its main properties, reference may be made to the following publication: Merck Index 20th edition (1996), no. 10220.
Swiss patent CH 368 267 describes compositions with a moisturizing effect which contain a pentose in combination with an amino acid. Xylose is mentioned among the pentoses as a product of hygroscopic character.
Within the framework of the present invention, it has now been discovered, surprisingly, that D-xylose, esters thereof and oligosaccharides containing xylose make it possible substantially and significantly to stimulate the synthesis and secretion of PG and GAG by human keratinocytes.
Thus. by virtue of their stimulating action on the synthesis of PG and GAG by the epidermal keratinocytes, D-xylose, esters thereof and oligosaccharides containing xylose can be used in cosmetic or pharmaceutical compositions, especially dermatological compositions, for topical application. making it possible inter alia to promote hydration of the skin, particularly of the epidermis, but also of tissues with a keratinocyte covering compartment, such as mucous membranes, particularly the lips, and also skin appendages, particularly the hair follicles.
D-xylose, esters thereof and oligosaccharides containing xylose can also be used to prevent or treat the effects of skin ageing, particularly the effects on the epidermis, which is the center of a large decline in PG and GAG content with age, being accompanied in particular by increased dryness of the skin.
D-xylose, esters thereof and oligosaccharides containing xylose can thus be used in any applications where it is desired to improve the synthesis of GAG and PG.
Thus, according to one of its characteristics, the invention relates to the use of a compound selected from the group consisting of D-xylose, esters thereof and oligosaccharides containing D-xylose as a cosmetic agent for stimulating the synthesis and/or secretion of proteoglycans (PG) and/or glycosaminoglycans (GAG) by the keratinocytes, especially the keratinocytes of the epidermis and the tissues with a keratinocyte covering compartment, such as mucous membranes, particularly the lips, and skin appendages, particularly the hair follicles, said agent being incorporated in a cosmetic composition comprising a cosmetically acceptable vehicle.
More precisely, it has been found that, because of their stimulating effect on the synthesis of GAG and PG by normal human keratinocytes, D-xylose and the compounds mentioned above make it possible:
to combat ageing of the epidermis. It is in fact known that ageing of the epidermis is largely associated with a loss of hyaluronic acid;
to combat drying of the skin associated with an insufficiency in the action of GAG, particularly hyaluronic acid. Said drying is observed especially on old skin and is associated essentially with a loss of hyaluronic acid;
to improve the tonicity of the skin. It has in fact been observed that an increase in the synthesis of GAG makes it possible to create a hydrated cellular environment which is favorable to exchanges of nutriments, ions, cytokine and growth factors secreted by epidermal cells. Such an environment is also favorable to the elimination of toxic metabolites. This effect therefore results in toned and healthy skin;
to maintain or restore the suppleness and elasticity of the skin. This effect is associated with stimulation of the synthesis of GAG, which makes it possible to create a hydrated environment for the matrical constituents, especially at the dermo-epidermal junction for favoring the microdisplacements between the elements of this matrix during mechanical stress. Such an effect therefore contributes towards creating a more supple and more elastic skin;
to improve the mineralization of the epidermis, thereby making the skin healthier and improving its vitality. This effect is associated with an improvement in the synthesis of GAG, which makes it possible to assure a good mineralization of the epidermis. In fact, via their charged groups, GAG can fix ions and contribute to the osmolarity of the epidermis. Here again, a good mineralization of the skin is synonymous with healthy skin of good vitality.
to facilitate intercellular exchanges. This effect can also be compared with simulation of the synthesis of GAG. which makes it possible to assure a correct differentiation of the epidermis since destruction of the hyaluronic acid causes opening of the intercellular spaces and epidermal acanthosis. This effect produces a more toned, denser and more compact skin;
to improve the three-dimensional structure of the dermo-epidermal junction. This can also be connected with an improvement in the synthesis of GAG, which makes it possible to assure the spatial organization of the matrical constituents, for example by strengthening the binding between laminin-6 and nidogen at the dermo-epidermal junction;
to facilitate healing without scar formation, thus making it possible to repair epidermal microtraumatisms which appear when there is a break in the continuity of the skin. Such an effect makes it possible to combat chapping and the cracked appearance of the skin;
to facilitate migration of the keratinocytes, allowing the formation of a corneal layer of good quality;
to modulate the action of the growth factors and the cytokines produced by the skin cells. Such an effect enables the cells to make use of the signals they need to assure their function.
According to one of its other characteristics, the invention further relates to uses of D-xylose and/or one of its esters for the manufacture of a pharmaceutical composition, especially dermatological composition, for treating insufficiencies in the synthesis or secretion of proteoglycans (PG) and/or glycosaminoglycans (GAG) by the keratinocytes, with a view to correcting the adverse effects of said insufficiencies and in particular to improving the functional state of the skin cells, especially the epidermal cells.
In particular, this pharmaceutical composition may be intended to facilitate healing and repair epidermal microtraumatisms, or to treat skin ulcerations, especially ulcerations on the legs, or to reduce the striae distensae of pregnancy.
In one particularly advantageous variant, D-xylose will be chosen as it has the advantage of being a commercial product.
However, it will also be possible to use one of its esters, particularly the D-galacturonic acid ester.
Esters of fatty acids comprising from 16 to 24 carbon atoms, particularly esters of natural fatty acids, may also be used advantageously.
Among these fatty acid esters, it will be advantageous to choose the esters of palmitic, stearic, oleic, linoleic, linolenic, arachidonic, erucic and lignoceric acids.
These fatty acid esters of D-xylose are of very particular interest in terms of the invention because, due to the presence of the fatty chain, they enable the xylose to penetrate the skin better by rendering the whole compound lipophilic. Furthermore, due to the presence of esterases in the skin, the xylose can be released in the skin, thus enabling these products to have the same advantages as D-xylose with regard to the synthesis and secretion of GAG.
Another family of compounds whose use proves to be of particular value in terms of the invention is the family of oligosaccharides containing xylose. According to the invention, oligosaccharide is understood as meaning sugar chains containing from 2 to 6 sugars.
According to the present invention, the oligosaccharide containing xylose will preferably be selected from those oligosaccharides as defined above which comprise at least one xylose and from 1 to 6 sugars. Such oligosaccharides are advantageously selected from xylobiose, xylobiose hexaacetate, methyl-xcex2-xylobioside, xylotriose, xylotetraose, xylopentaose and xylohexaose.
The oligosaccharides will preferably be xylobiose, which is made up of two xylose molecules joined by a 1,4 linkage, and xylobiose acetates such as xylobiose hexaacetate.
These oligosaccharides are of particular value within the framework of the invention because they can be degraded gradually in the skin by the numerous osidases present, and can thus release xylose. Therefore, in a manner of speaking, these oligosaccharides containing xylose act like xylose precursors and constitute true reservoirs of xylose to be released over a period of time.
In both the cosmetic and the pharmaceutical compositions of the invention, the D-xylose, esters thereof or precursors of the oligosaccharide type defined above will advantageously be present at a concentration of between 0.001 and 5% by weight, preferably of between 0.01 and 0.5% by weight, based on the weight of said composition.
In general, the compositions of the invention will advantageously be formulated for topical application, particularly as emulsions, lotions, gels, lipsticks or mascaras.
In another variant of the invention, the cosmetic or pharmaceutical composition, especially dermatological composition, may comprise liposomes, the D-xylose, D-xylose ester or oligosaccharide containing xylose being either outside said liposomes or partially or totally incorporated inside said liposomes.
Finally, in one particularly valuable variant of the invention, the D-xylose, esters thereof or precursors of the oligosaccharide type defined above may be combined, in the composition of the invention, with a number of active principles such as:
amino sugars, particularly D-glucosamine and D-galactosainine;
amino acids, particularly L-serine or any extract containing it, especially extracts of algae;
sodium ascorbate (vitamin C) and derivatives thereof such as the phosphate, palmitate, acetate or propionate;
vitamin A (also called retinol) and esters and derivatives thereof, particularly the palmitate, acetate and propionate;
madecassic acid, asiatic acid and glycosylated derivatives thereof,
B group vitamins, particularly vitamins BI, B6 and B12, and folic acid;
vitamin PP;
forskolin, derivatives thereof and extracts of Coleus forskolii;
salicylic acid and derivatives thereof, particularly those with lipophilic chains;
ecdysterone and derivatives thereof, particularly the acetates;
retinoids, particularly retinoic acid, retinaldehyde and retinyl phosphate;
micronutrients such as silica and derivatives thereof like silanol, magnesium and salts thereof and manganese and salts thereof,
extracts of Potentilla erecta;
extracts of fruits, particularly apple and lemon and especially apple juice or its polyphenols;
phosphodiesterase inhibitors, particularly xanthines;
extracts of Siegesbeckia orientalis_or daturoside;
extracts of Centella asiatica enriched in triterpenes;
extracts of Bertholletia;
chliorogenic acid. caffeic acid, sinapic acid, and caffeoylquinic acid;
free radical inhibitors, particularly procyanidolic oligomers, extracts of green tea and grape seeds, nordihydroguaiaretic acid (NDGA), curcumin extracts and curcuminoids.
According to another of its essential characteristics, the invention further relates to a method of cosmetic or pharmaceutical treatment wherein it is sought to stimulate the synthesis and/or secretion of proteoglycans (PG) and/or glycosaminoglycans (GAG). According to this method, an effective amount of D-xylose, one of its esters or an oligosaccharide containing D-xylose, as defined above, is applied to the part of the body in question in order to stimulate said synthesis and secretion.
The compositions used in these methods of treatment are those described above.
According to another essential characteristic, the invention further relates to the use of a D-xylose ester, particularly the D-galacturonic acid ester or one of the fatty acid esters of D-xylose as defined above, or an oligosaccharide containing D-xylose, particularly an oligosaccharide as defined above, as a cosmetic agent for hydrating the basal layer of the epidermis.
According to another feature, the invention further relates to the use of a D-xylose ester, particularly the D-galacturonic acid ester or one of the fatty acid esters of D-xylose as defined above, or an oligosaccharide containing D-xylose, particularly an oligosaccharide as defined above, for the manufacture of a pharmaceutical composition, especially dermatological composition, for treating insufficiencies in the hydration of the basal layer of the epidermis.
The Examples which follow are given purely by way of illustration of the invention.